Lifting a balloon with heated air
The Montgolfier brothers conducted a series of hot-air balloon experiments in 1783. Heated air has a lower density; inside a sufficiently large envelope, buoyancy can lift the envelope and its load. Material weight, heating and the enclosure all affected whether the balloon would rise.
In September they sent a sheep, a duck and a rooster aloft at Versailles; the animals landed alive. Pilâtre de Rozier then took part in tethered ascents, putting a person in control of a balloon in the air.
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Two passengers above Paris
On November 21, 1783, de Rozier and the Marquis d’Arlandes rose over Paris in a Montgolfier balloon. Once released from its restraints, it travelled with the wind. The passengers maintained the heated air by tending the fuel as they flew above the city.
The flight lasted about 25 minutes and covered roughly nine kilometres before landing. Unlike the preceding tethered trials, its occupants travelled freely away from the starting point.
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Franklin records the flight
Benjamin Franklin, then in France, described the flight in a letter written that day to Joseph Banks, president of the Royal Society. He recorded the balloon’s appearance and the passengers’ actions, and considered uses for a machine that could carry people into the air.
He also discussed how wind determined its course. Heating could regulate ascent and descent, while directed horizontal travel required additional propulsion and control, a problem later addressed by airship design.
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Flight becomes a repeatable practice
Ballooning made human flight an experimental activity. An envelope, heating equipment and a platform formed a craft that could be built, launched and recovered. In December 1783, Charles and Robert made a free flight in a hydrogen balloon, developing another lighter-than-air approach.
Balloons later carried observers and travellers who recorded altitude, weather and routes. The Paris flight left named participants, letters and images, as well as experience that could be used in building the next craft.
References: [1]